Enhance App Icon handling of 256 and 512 pixel PNG icon sizes

[cocobean]

Windows and Mac include icon sets from 16 to 256 pixels in size. PNG icon sets includes images up to 512 pixels in size.

NOTE: Windows standard icon sizes are 16, 32, 48 and 256. Apple Mac OS X supports these icon sizes for app icon development:

    512x512 pt (512x512 px @1x, 1024x1024 px @2x)
    256x256 pt (256x256 px @1x, 512x512 px @2x)
    128x128 pt (128x128 px @1x, 256x256 px @2x)
    32x32 pt (32x32 px @1x, 64x64 px @2x)
    16x16 pt (16x16 px @1x, 32x32 px @2x)

[pulkomandy]

We use vector icons which scale to any resolution.

[X512]

We use vector icons which scale to any resolution.

Haiku-compatible vector icons are often not provided by application developers. Raster icons (often with multiple sizes) are always available. Not all developers have enough skills to make HVIF icons.

[X512]

Raster bitmap embedding can be implemented in HVIF to solve this issue. HVIF already support LOD levels.

[axeld]

The original plan was also to simply allow to put PNGs into BEOS:ICON; the API should already be type agnostic.